The present invention is concerned with improving a specific known process carried out in a specific known rotary kiln processor, to recover hydrocarbons from oil sand. This processor is known in the industry as the "ATP processor" and will be referred to in this disclosure by that terminology. In the claims, the processor is referred to as "a rotary kiln processor". The process and processor are further described in U.S. Pat. No. 4,280,879, issued to William Taciuk. The oil sand referred to comprises sand associated with water and bitumen hydrocarbons containing sulfur.
The present invention is directed toward suppressing sulfur dioxide emissions from the processor. Relevant prior art processes are disclosed in Canadian Patent No. 1,156,953, issued to Kessick et al (modifying sulfur in coke) and in U.S. Pat. No. 4,424,197 issused to Powell et al (SO.sub.2 capture).
Returning to the ATP processor, it comprises inner and outer, generally tubular members herein referred to as tubes. The tubes are generally coextensive, concentric, spaced apart and horizontal. They are interconnected so as to form a unitary rotatable assembly. Stationary end frames seal the first and second ends of the outer tube. Drive means are provided for rotating the outer tube, and thus the entire assembly, about its longitudinal axis. A passageway extends longitudinally through the inner tube and an annular passage is formed between the tubes. The inner tube passageway is closed at its first end by a stationary end frame and at the second end by a vertical closure plate. It is divided along its length by an upright baffle, thereby creating two segregated sequential chambers or "zones" which combine to extend between the first and second ends of the inner tube. The zone at the first end is referred to as the "preheat zone" and that at the second end as the "vaporization zone". A feed stream comprising particulate solids may be fed into the first end of the preheat zone by means of a conveyor extending through the first end stationary end frame. As the tube assembly is rotated, this feed is advanced longitudinally through the inner tube passageway. As it is advanced, the feed is simultaneously cascaded. In addition, as it moves through the preheat zone the feed is heated by heat exchange with the wall of the inner tube. The inner tube is heated by hot solids and flue gases moving countercurrently through the annular space. (The manner in which the hot solids and flue gases are provided is described below). As a result of progressive heating of the feed during its advance through the preheat zone, contained water is vaporized. The produced steam is suctioned from the preheat zone by a gas compressor and conduit assembly communicating with the zone at its first end. Thus, in the preheat zone the solids are mixed as they cascade, the feed is progressively heated and water is vaporized, and the atmosphere in the vicinity of the baffle is caused to be substantially oxygen-free, due to the back flow of steam. The preheated feed is discharged from the preheat zone through helical chutes extending through the baffle. The chutes lead into the vaporization zone. On entering the vaporization zone, the preheated feed is mixed with hot solids recycled from the annular space. As a result, the feed is now heated to a relatively high temperature. The hydrocarbon associated with the solids is therefore vaporized and thermally cracked and some coke is formed on the solid particles. A second gas compressor and conduit assembly, communicating with the second end of the vaporization zone, suctions the hot gases from the zone and draws them through a condenser. The coked solids are discharged from the second end of the vaporization zone by means of a helical chute extending through the closure plate at the second end of the inner tube. The coked solids are discharged into the second end of the annular space. The annular space provides combustion and cooling zones extending sequentially from the second end to the first end thereof. Air is injected through the second stationary end frame into the combustion zone. In addition, a gas burner also extends through the second end frame and supplies supplemental heat to the combustion zone. Lifters extend inwardly from the inner surface of the outer tube along its length. In the combustion zone, these lifters lift and drop the coked solids through the injected air stream. In the course of this, the coke combusts, producing flue gases, and the solids are further heated. The resulting hot solids are advanced longitudinally through the annular space from its second end toward its first end. A portion of these hot solids are recycled, by means of a helical chute, from the first end of the combustion zone into the first end of the vaporization zone, as was previously described. The balance of the hot solids advance into the annular cooling zone, which is coextensive with the preheat zone of the inner tube. Here the hot solids are repeatedly lifted and dropped onto the outer surface of the preheat section of the inner tube. Thus the preheat section is heated by contact with the shower of hot solids and the flow of hot flue gases moving through the cooling zone. At the same time the hot solids and flue gases are correspondingly cooled, thus recovering useful heat from them. The cooled solids are discharged from the cooling zone through the first end frame by means of a chute. The flue gases are removed from the annular space by a fan and conduit assembly communicating with the first end of the annulus.
In summary then, the ATP processor carries out the following when fed oil sand:
progressively preheating the oil sand feed by heat exchange through the tube wall to vaporize the water contained in the feed; PA1 pyrolysing the preheated feed in the vaporization zone by mixing it with recycled hot combusted sand, thereby vaporizing and thermally cracking hydrocarbons entrained in the feed, to produce coked sand and oil vapours; PA1 transporting hot solids into and out of the vaporization zone by means of chutes, essentially preventing the movement of vapours from and into the zone; PA1 heating and burning the coked sand in the combustion zone, to provide a portion of the process heat and produce clean hot sand; PA1 recycling part of the hot sand into the vaporization zone to provide required heat; PA1 separately collecting the steam and hydrocarbon vapours from the preheat and vaporization zones and separately condensing them to yield in the second case an oil fraction in liquid form; PA1 lifting and dropping hot sand onto the inner tube wall in the cooling zone, to supply required heat to the tube wall for conduction into the preheating zone; PA1 discharging clean sand from the cooling zone as a tailings stream; and PA1 discharging flue gases from the annular space for treatment as a waste stream. PA1 combining calcium oxide or calcium hydroxide to a heavy oil containing sulfur in the molar ratio of calcium to sulfur in the feed ("Ca:S") of 1:1 to 1:3 to form a mixture; and PA1 coking said mixture to form coke having a decreased tendency to produce SO.sub.2 (capturing up to 80% of the sulfur-containing gases) upon subsequent combustion in air. PA1 contacting SO.sub.2 -containing gas in a fluidized bed or packed column reactor of highly porous particles of calcium oxide; and PA1 reacting the SO.sub.2 -containing gas with the calcium oxide at 500.degree. to 1000.degree. C. to form calcium sulfate ("CaSO.sub.4 "). PA1 bitumen is never segregated into a liquid form for mixing with sulfur modifying reagents; PA1 the whole oil sand feed is subjected to, retorting conditions; PA1 gases produced from retorting are not intimately contacted with sulfur modifying reagents, as is the case with fluidized bed cokers; PA1 coked byproducts, produced from retorting, are formed as a layer upon inorganic solids, typically comprising fewer than 10 weight % on the solids; PA1 coked byproducts are combusted in a low density particle cascading combustion zone, not in a dense, fluidized bed combustor. PA1 adding CaO to oil sand containing sulfur, to provide a continuous processor feed stream; PA1 advancing the processor feed stream through the preheat zone of the ATP processor, thereby dispersing the added CaO throughout the feed, forming a mixture, progressively heating the feed from ambient temperature to about 250.degree. C., and vaporizing any water in the feed; PA1 suctioning the gases produced in the preheat zone using compressor and conduit means communicating with the first end of the said zone, whereby there is a back flow or countercurrent movement of the produced gases, relative to the direction of advance of the feed; PA1 advancing the preheated feed stream into the vaporization zone and mixing it therein with recycled hot solids to raise the temperature of the feed above about 480.degree. C., preferably to about 525.degree. C., thereby vaporizing and cracking contained oil and forming coked solids containing calcium and sulfur compounds; PA1 suctioning produced gases from the second end of the vaporization zone and condensing them to yield liquid condensate; PA1 advancing the coked solids into the combustion zone, injecting air and adding heat to said zone to burn coke and yield hot solids preferably having a temperature of about 730.degree. C. and producing flue gases containing substantially no SO.sub.2 ; PA1 recycling a sufficient portion of the hot solids from the first end of the combustion zone, into the first end of the vaporization zone, to heat the feed stream as previously stated; PA1 providing chutes at the first and second ends of the vaporization and combustion zones, providing movement of solids from zone to zone, essentially preventing the movement of vapours from leaving the vaporization zone, or oxygen containing gases from entering the vaporization zone; PA1 advancing the balance of the hot solids and flue gases through the cooling zone and lifting and dropping the hot solids onto the preheat tube to heat the feed stream passing therethrough and to cool the solids passing through the cooling zone; PA1 discharging the solids reaching the first end of the cooling zone; and PA1 suctioning gases from the first end of the cooling zone, removing entrained solids, and condensing waters of combustion to yield solids, liquid condensate, and waste gases substantially free of SO.sub.2. PA1 continuous cascading or mixing of fresh oil sand and CaO in the preheat zone is conducted to achieve a desirable mixing of the CaO throughout the widely dispersed bitumen, a portion of the CaO becoming hydrated to calcium hydroxide ("Ca(OH).sub.2 "); PA1 advancement of the oil sand mixture to the vaporization zone and mixing it with a recycle stream of hot coked solids, to raise the temperature of the feed stream sufficiently so that hydrocarbons are pyrolysed and the product is suctioned from the zone as a gas, thereby separating the hydrocarbons and forming coked product on the solids; PA1 in conjunction with the pyrolization, the CaO and Ca(OH).sub.2 react to become intimately associated in a modified calcium product form with the coked product; PA1 after pyrolization, the coked product is combusted in the combustion zone, the modified calcium product acting to capture substantially all of the sulfur released from the combusted coke to yield a flue gas product substantially free of SO.sub.2, and a stable calcium-sulfur product associated with the solids; and PA1 a portion of the coked product and residual modified calcium product which is recycled to the vaporization zone as previously stated.
This known process, as just described, is referred to in the claims as "process comprising treating oil sand . . . in a rotating kiln-type processor to recover hydrocarbons".
Unfortunately, the combustion of coke in the ATP processor is accompanied by troublesome production of sulfur-containing gases. A portion of the sulfur, originating from the feed bitumen, ends up in the coke. When combusted, the sulfur-containing coke releases SO.sub.2 with the flue gases, requiring expensive flue gas treatment equipment to remove the environmentally noxious gas.
Turning now to the prior art Kessick et al process, it involves:
Several functional differences between the process of Kessick et al and the ATP processor raised questions of whether adequate sulfur capture could be achieved with the low Ca:S ratios disclosed. Firstly, a capture of only 80% would be insufficient to permit elimination of the SO.sub.2 removal equipment. Secondly, in contrast to Kessick et al, the bitumen (heavy oil) component of the ATP processor feed is widely dispersed on about ten times its weight of solids, further casting doubt on the capabilities of even achieving an 80% capture. Lastly, Kessick et al did not anticipate retorting in the unconventional vaporization zone of the ATP processor; greater contacting densities of a delayed or fluidized bed coker being preferred.
The prior art Powell et al process involves:
Early experiments, which attempted direct application of the process of Powell et al to the ATP processor, resulted in unsatisfactory results. Addition of calcium oxide to the combustion zone resulted in only about a 60% capture of sulfur-containing gases which was insufficient to suggest elimination of the expensive SO.sub.2 removal equipment.